1. Field of the Invention
The present invention relates to a switch structure for a car electrical part such as a lamp unit to be mounted on the ceiling portion of a car room.
2. Description of the Related Art
As known well, on the ceiling portion of a car room, there are mounted electrical parts such as a room lamp and a map lamp. Also, on a door trim, there are mounted electrical parts such as a switch for a power window and a foot lamp.
Description will be given below of a switch structure used in a conventional electrical part for use in a car with reference to FIGS. 3 and 4A to 4C. FIG. 3 is an exploded perspective view of a conventional switch structure. FIG. 4A is a plan view of the conventional switch structure, showing its switch-off state, FIG. 4B is a section view thereof, showing its switch-off state, and FIG. 4C is a section view thereof, showing its switch-on state.
As shown in FIGS. 3 and 4A to 4C, in the conventional switch structure, terminal members 2, 3 and 4, which are respectively connected to a function member (not shown) such as a light bulb holder, are disposed and held at given positions on a base member 1 which is formed of insulating resin. In the two end portions of each of the two terminal members 2, there are formed a wire connecting portion 2B, into which an insulated covered wire can be pressure inserted, and a tongue-shaped contact portion 2A for contact with a movable contact piece 5. In the two ends of the terminal member 3 forming part of the light bulb holder, there are respectively formed a wire connecting portion 3A and a plate-spring-shaped portion (not shown). Similarly, in the two ends of the terminal member 4 forming part of the light bulb holder, there are respectively formed a contact portion 4A for contact with the movable contact piece 5 and a bent portion (not shown) A light bulb (not shown) is held by and between the plate-spring-shaped portion of the terminal member 3 and the bent portion of the terminal member 4.
The movable contact piece 5 has a substantially-U-shaped section, can be fitted with a guide rail 1C formed in the vicinity of one end of the base member 1, and is able to slide on the guide rail 1C. Also, in the movable contact piece 5, there is formed a plate-spring-shaped contact portion 5A which can be selectively contacted with a portion between the contact portion 2A of one terminal member 2 and the contact portion 4A of the terminal member 4, only the contact portion 4A of the terminal member 4, and a portion between the contact portion 2A of the other terminal member 2 and the contact portion 4A of the terminal member 4; and, on the contact portion 5A, there is provided a projection 5B which is used to generate a click feeling. Also, in the guide rail 1C as well as in the contact portions 2A, 4A of the terminal members 2, 4, there are formed uneven portions which can be engaged with the projection 5B. The movable contact piece 5 can be engaged with a switch operation knob (not shown) and thus can be slid between the above respective contact positions in response to the movement of the switch operation knob.
As known well, since there is formed a fit clearance between the movable contact piece 5 and the guide rail 1C of the base member 1, in the conventional switch structure for a car electrical part, in order not only to be able to absorb the rickety motion of the movable contact piece 5 caused by the fit clearance but also to be able to secure a given contact pressure between the contact portion 5A of the movable contact piece 5 and the contact portions 2A, 4A of the respective terminal members 2, 4, the contact portion 5A is formed in a plate-spring-like shape and also there is formed the projection 5B used to generate a click feeling. However, because the contact portion 5A and projection 5B are disposed in one and the same portion, in case where the switch operation knob is operated, there is a possibility that, in the above fit clearance portion, the movable contact piece 5 can be rotated about the projection 5b in the axial direction of the movable contact piece 5. In case where the movable contact piece 5 is rotated about the projection 5b, there is raised a possibility that the contact portion 5A cannot be properly contacted with the contact portions 2A, 4A of the respective terminal members 2, 4, which results in the poor contact between them. Also, there are raised another possibilities: that is, the edge portions 5C of the movable contact piece 5 can be contacted with the guide rail 1C of the base member 1 to thereby cut the base member 1 and thus produce resin chips; and, the sliding resistance of the movable contact piece 5 can be increased to thereby degrade the operation feeling of the switch operation knob accordingly.
The present invention aims at solving the above-mentioned problems found in the conventional structure. Accordingly, it is an object of the invention to provide a switch structure for a car electrical part which not only can reduce the possibility of poor contact occurring between the terminal members and movable contact piece but also can provide an excellent switch operation feeling.
In attaining the above object, according to the invention, there is provided a switch structure for a car electrical part comprises: two or more terminal members each having one end connected to a function member or a wire member and the other end serving as a terminal-side contact portion; a movable contact piece contactable selectively with the terminal-side contact portions to thereby form a switch; and, a base member including a terminal hold portion for arranging and holding the terminal members thereon in such a manner that the terminal-side contact portions have a given position relationship, and a guide rail portion which can be engaged with and holds the movable contact piece in such a manner that the movable contact piece is able to slide in a given direction, wherein the movable contact piece includes two contact-piece-side contact portions disposed perpendicular to the sliding direction of the movable contact piece for contact with the terminal-side contact portions, and a spring portion which, when it is elastically deformed, can be contacted with the guide rail portion of the base member and, due to its elastic force, can generate a given contact force between the contact-piece-side contact portions and terminal-side contact portions.
In the above switch structure, preferably, in part of the spring portion of the movable piece, there may be disposed a projection and, in the portion of the guide rail portion of the base member on which the spring portion of the movable contact piece is slidable, there may be disposed an uneven portion engageable with the projection of the spring portion in order that the contact-piece-side contact portions and the terminal-side contact portions can be contacted with each other in a given selective state.
Also, preferably, the spring portion of the movable contact piece may be contacted with a different surface of the base member from the surface thereof that holds the terminal members thereon.
Further, preferably, the movable contact piece may be structured such that: a section thereof in a direction perpendicular to the sliding direction of the movable contact piece has a substantially U-like shape; in one of two sides thereof forming a substantially U-like shape and opposed to each other, there are disposed the above-mentioned contact-piece-side contact portions; and, in the other side, there is disposed the above-mentioned plate-spring-shaped portion.
In addition, preferably, at least one of the above-mentioned contact-piece-side contact portions and the above-mentioned plate-spring-shaped portion may be disposed at a position distant from the operation point of the operation force applied to the movable contact piece.